MD Downloads: declare/initialize ActionService#searchTerms_ in ctor

chrome/browser/resources/md_downloads/action_service.js

Index: chrome/browser/resources/md_downloads/action_service.js
diff --git a/chrome/browser/resources/md_downloads/action_service.js b/chrome/browser/resources/md_downloads/action_service.js
index 3294632cb469e660a8dd48be742a21c41370f358..e065ee9d97ffde466a8a9b00f098c7d30f8aa495 100644
--- a/chrome/browser/resources/md_downloads/action_service.js
+++ b/chrome/browser/resources/md_downloads/action_service.js
@@ -12,7 +12,10 @@ cr.define('downloads', function() {
   }
 
   /** @constructor */
-  function ActionService() {}
+  function ActionService() {
+    /** @private {Array<string>} */
+    this.searchTerms_ = [];
+  }
 
   /**
    * @param {string} s
@@ -36,9 +39,6 @@ cr.define('downloads', function() {
   };
 
   ActionService.prototype = {
-    /** @private {Array<string>} */
-    searchTerms_: [],
-
     /** @param {string} id ID of the download to cancel. */
     cancel: chromeSendWithId('cancel'),